A. Field of the Invention
The present invention relates to a shock suppressing apparatus and method for a shoulder-fired rocket launcher.
B. Brief Description of the Prior Art
A typical prior art shoulder-fired rocket launcher comprises an elongate tube which in its firing position is placed on the shoulder of the operator, with the forward end (through which the rocket is discharged) being positioned several feet forward of the operator's head, and with the rear end being a short distance rearwardly of the operator's head. The rocket itself is located in the rear end of the launch tube, and the rocket nozzle is closed by a plug. Upon ignition, there is a very rapid pressure build up in the rocket propellant chamber, and at a predetermined design pressure level, the nozzle plug is expelled from the nozzle rearwardly at a high velocity, generally in the supersonic range. The rocket is then propelled forwardly through the tube toward its intended target, with the exhaust of the rocket being emitted outwardly from the rear end of the launch tube. The noise pulse which is generated is at a level that requires the weapon user to wear ear plugs and ear muffs to protect his hearing. Even when using such protective equipment, the noise pulse is at the maximum upper limit that can be tolerated by humans. Thus, a technology barrier exists which prevents the development of increased performance systems.
To reduce the ignition noise level, considerable research has been conducted to optimize the pressure level and propellant burn time reached before the plug is expelled. This research has been successful in varying these parameters; however, it has not been successful in reducing the noise level to any significant extent.
Another prior art attempt to reduce the noise level is based on energy conversion. One example of this is illustrated by the "Armbrust Weapon System". The basic technique is to both perform mechanical work and to contain the gases generated by the firing inside a pressure vessel. In this system, both the missile and an inert mass are enclosed in a pressure chamber of a launch tube, with a motor being placed between the missile and the inert mass. When the weapon is fired, the missile and the inert mass move in opposite directions to minimize recoil, and the motor exhaust products are trapped inside the pressure chamber. The gases are released over a relatively long period of time, with the noise being reduced by trapping the exhaust gases and releasing them over a long period of time. While the approach used in this system is effective, it has several severe drawbacks. First, it is heavy since the missile and the inert mass must have approximately the same mass, and the pressure chamber must be strong enough to hold the motor exhaust products. Thus, this apparatus is approximately twice as heavy as a conventional rocket system. Also, it is expensive to fabricate.
Some experimental work has been done to solve this noise problem by utilizing classical muffler design techniques. However, this work indicates that such muffling devices are too large for practical utility. Further, such devices are not effective for solving the peak noise problem.
There also have been some attempts to utilize techniques which have been effective on large jet and rocket engines, and also techniques utilized in recoilless weapons. Such techniques included the use of wire screens, multiple nozzles and fingers placed in the exhaust stream. Such techniques are effective in disrupting the steady state noise condition that occurs after the peak ignition transient. However, such techniques did not prove to be effective in resolving the peak noise problem.
A review of the patent literature disclosed various devices which are attached to rocket launchers or other weapon system to affect the flow of exhaust gases which are emitted. However, to the best knowledge of the applicants herein, none of these devices are adequately effective in reducing the peak noise levels in a shoulder-fired missile system. The U.S. Patents noted in a search of the prior art are noted below.
U.S. Pat. No. 2,466,714, Kroeger et al, discloses a recoilless firearm which can be shoulder mounted. The propellant charge is located in a perforated cylinder. When the propellant is ignited, frangible covers over holes are blown out and gases are released from the perforated cylinder. A nozzle provides a forward impulse to the rocket launcher counter-acting the recoil generated by the acceleration of the missile down the launch tube. The noise sources for this device are similar to those of a similar rocket system, with a substantial initial shock being emitted from the multiple openings. Analysis indicates that this device would not be adequate to effect any substantial reduction of peak noise levels.
U.S. Pat. No. 2,489,747, Burney, discloses a gun which is designed to reduce recoil. This device uses the thrust generated by burning an excessive powder charge and allowing the gases to escape through a rather standard divergent nozzle to affect the recoil generated by the motion of a projectile down the barrel. A screen is placed in front of the nozzle to keep the burning propellant inside the combustion chamber. Analysis indicates that the noise sources of this system are not significantly different than would be expected from a standard rocket motor.
U.S. Pat. No. 2,489,748, Burney, discloses a device having basic similarities to the patent of the same inventor noted immediately above. Analysis indicates that the sound characteristics of this device would be the same as that in the first mentioned Burney patent.
U.S. Pat. No. 2,866,316, Towle et al, discloses a thrust reversing and sound suppressing device for a jet engine. The exhaust of the engine is released to the atmosphere through multiple individual nozzles, with the primary effect being to break up the simple jet stream from the power plant into a number of smaller jets. Analysis indicated that this would not be effective in significantly reducing the peak noise generated by a rocket launcher such as that for which the present invention is adapted.
U.S. Pat. No. 2,986,973, discloses a device which is entitled, "Low-Recoil, Variable-Range Missile Projector". The objectives of this device are to reduce recoil and to provide a means to vary the range of the projectile without changing the elevation angle or changing the propellant charge. A countercharge is burned in a chamber which has a number of holes on the sides. The gases propel the missile down and out the tube, with hot gases escaping normal to the axial flow through orifices which split the escaping gases in a forward and aft direction, thereby neutralizing the recoil. Analysis indicates that each of the vent openings and nozzles would be a separate noise source and thus would be a relatively complex noise producer rather than a noise suppressor.
U.S. Pat. No. 3,035,494, discloses a recoil adjust device for a weapon system. Specifically the device incorporates a mechanism to compensate for wear, erosion, or fouling of the nozzles or other openings in the recoil system by changing the position of an adjustable compensator. The compensator functions as a preliminary gas flow restrictor placed ahead of the choked venturies. As the adjustable compensator or other elements wear, the compensator is adjusted to reduce the gap between the compensator and the chamber wall, thereby restoring the original flow conditions necessary to eliminate or compensate for the recoil of the system. Analysis indicates that the sound characteristics of this device do not differ significantly from the characteristics of a standard rocket motor, with each separate venturi or nozzle being a separate noise emitter.
U.S. Pat. No. 3,129,636, Strickland et al, shows a projectile launching system designed to eliminate recoil. There is a nozzle plug which is attached to the projectile. Since the effective area of the nozzle plug is less than the effective area of the projectile, the pressure generated after ignition causes the projectile to be accelerated down the launch tube. With regard to the noise generated by this device, analysis indicates that as soon as the nozzle plug was removed, the propellant gases go through a standard convergent/divergent underexpanded nozzle. It is anticipated that there would be no significant suppression of an initial pressure wave generated from the nozzle.
U.S. Pat. No. 3,208,384, Fountain, shows a rocket launching system adapted to be mounted to an aircraft. The objective of this particular device is to both neutralize the thrust of a rocket motor and to deflect the hot gas flow forward and aft to prevent the hot gases from damaging the surfaces of the aircraft to which the launcher is attached, in the event of an accidental ignition. The gases generated by the rocket motor are turned 90.degree. and emitted through numerous gas escape orifices perpendicular to the center line of the missile. This neutralizes the thrust. The deflector spreads the gases into forward and aft components, thereby protecting the aircraft from damage by the hot propulsive gases generated by the rocket motor. Analysis indicates that this device would not be effective in obtaining a significant decrease in peak noise suppression.
U.S. Pat. No. 3,380,340, Bergman et al, discloses a weapon system designed to decrease recoil. The propellant is contained in a pressure chamber that is centered and supported in the launcher by a number of centering supports. The launcher itself is fitted with a nozzle designed to provide a force in the forward direction if high pressure gases are released through it to the atmosphere. The high pressure chamber is also fitted with a nozzle for the purpose of providing a force in the forward direction as gases escape through it to the atmosphere. Both the launcher and the pressure chamber nozzles contain plugs designed to break at the same gas pressure at which the shear pin that attaches the projectile to the launcher breaks. When the weapon is fired, the propellant burns and the gas escapes from the holes in the pressure chamber. The pressure inside the launcher increases up to the point where the shear pin is broken, and the gases begin to escape through both the pressure chamber and launcher nozzles to offset the recoil created by the reaction of the projectile. Analysis indicates that escaping gases impinging on the projectile sets up a shock wave that is a primary sound source. This would be followed by a pressure wave from the front of the launcher. Gases escaping from the front of the launcher would create a noise source. When the nozzle pressure plugs burst or are ejected, a series of shocks will be set up by the escaping debris or plugs, followed by an overpressure wave originating from the combined effect of both nozzles. It is not expected that this would result in any decrease of noise, and could under some circumstances actually increase the noise level of the launcher.
U.S. Pat. No. 3,490,330, Walther, describes a projectile launching system which reduces recoil and noise by combining the use of a pressure chamber and using multiple small orifices. When the propellant charge is ignited, the gas acts against a piston which in turn pushes the projectile down the launch tube. At the exit end of the tube, there is an interceptor which retains the piston, so that the piston thereby plugs the front end of the launch tube to prevent propellant gases from escaping from the front of the launcher. The launcher, therefore, acts as a pressure vessel, and the propellant gases are vented to the atmosphere through a series of nozzles. This system reduces the impulse noise by greatly increasing the time period over which the propulsive gases are released to the atmosphere and by breaking up the single exhaust flume into a large number of separate sources.
U.S. Pat. No. 3,505,958, Vilvajo, discloses a weapon system designed to eliminate recoil by firing one charge to accelerate the projectile toward the target, and at the correct point in time firing a second charge that is exhausted in the opposite direction through a nozzle, thereby producing a forecoil that equals the recoil generated by the projectile. The patent pertains to the delay fusing system and does not address itself to the problem of noise generated at firing. Analysis indicates that this device would generate a complex noise pattern made up of a noise generated by the shock from the projectile, the initial overpressure wave and the transonic shear layer. This would be followed at a later time by an initial overpressure wave and noise from the transonic shear layer from the second rocket motor firing. It is anticipated that this device is a noise generator instead of a noise suppressor.
U.S. Pat. No. 3,561,679, Lager, discloses a collapsible nozzle, the objecting being to reduce the size of the rocket nozzle by collapsing it, and then having the nozzle expand to its operating condition after the motor is ignited. The noise sources of this device are substantially the same as those of a rocket using a conventional noncollapsed nozzle. Analysis indicates that this would have no significant effect in reducing noise.
U.S. Pat. No. 3,745,876, Rocha, discloses an anti-tank weapon that has a launch tube which can be collapsed into a small easily-carried package. When the weapon is to be used, the launch tube is extended and the weapon fired from the shoulder in a conventional manner. Analysis indicates that as the gases move down the tube, there would be no signficant reduction in peak noise level.
U.S. Pat. No. 3,815,469, Schubert et al, discloses a launching system for missiles, particularly anti-tank projectiles, which is similar to the Armbrust system discussed previously herein. When the propellant is ignited, the gases react against two pistons. The projectile is accelerated down the launch tube in a conventional manner. When the projectile exits from the launch tube, the piston is captured by an interceptor at the forward end of the tube, and the forward end of the launch tube is thus sealed, thereby making the launch tube a pressure container. At the same time the second piston is driven toward the aft end of the launcher to cause an expendable mass or jelly to be extruded through a plurality of inverse nozzles. The momentum of the jelly mass is designed to equal the projectile momentum, thereby cancelling out the recoil. When the jelly is expended, the piston seals the jelly nozzles, thereby completing the seal on the launch tube as a pressure bottle. The gases are then allowed to decay to atmospheric pressure over a long period of time, thereby reducing the sound.